1. Field of the Invention
The present invention relates to a filter device, especially to a filter device with an optical filter.
2. Description of the Prior Art
A camera, especially a monitoring camera, comprises a camera lens, a photographic sensing device and a conventional filter device. The photographic sensing device provides an optical sensing element such as a negative or a charge-coupled device (“CCD”). The filter device is mounted between the camera lens and the sensing element of the photographic sensing device. The filter device is used to filter and adjust a light coming into the camera through the camera lens aiming for the sensing element of the photographic sensing device. The conventional filter device may have for example a transparent lens and a colored lens. The lenses selectively switch in daylight or at night so that the light passing through the lens exposes the sensing element of the photographic sensing device in a proper intensity.
The conventional filter device having multiple lenses is driven by a driving device to align a desired lens with the camera lens and the sensing element. An embodiment of the conventional driving device is a driving motor allowing lenses of the filter device to slide to a position for alignment. However, the size of the driving motor makes it infeasible to minimize the filter device.
Taiwan utility patents No. M253792 and M302047 provide minimized filter devices. The minimized filter device has a coil wound around the lenses and magnetic elements corresponding to the coil. The coil carrying electric currents generates magnetic flux and applies magnetic force on the magnetic elements to drive the lenses to slide. Thus desired lens is slide to a position allowing alignment with the camera lens and the sensing element. Such simple structure makes minimized filter devices possible.
However, abrasion occurs while the coil slide against other element within the minimized filter device. The coil may be worn-out and cause failure. Although the minimized filter device provided by the patent No. M302047 has an additional positioning track preventing the coil to break by yanking from an outer wire, the positioning track fail to prevent the coil from wearing-out. The worn-out failure problem of the minimized filter device is apparent.
In an ecological aspect, both the aforementioned conventional filter device and the minimized filter device require constant electric power supply during whole operating process. The driving motor and the coil consume power continuously even when they are not driving the lenses to slide. It is obvious that the current market goes for minimized and power-saving products. Solving the power-wasting problem is expected to bring commercial competitiveness and global good in the ecological aspect.
To overcome the shortcomings, the present invention provides a filter device to mitigate or obviate the aforementioned problems.